Aluminum multi-port microchannels are currently utilized in automotive air conditioners for refrigerant
condensation. In general, research activities are directed towards developing other air conditioning and refrigeration
systems with microchannel condensers and evaporators by analyzing heat exchanger performance parameters of heat
transfer, pressure drop, and void fraction.
The purpose of this particular study is the experimental investigation of frictional pressure drop and void
fraction in microchannels. Experiments are performed using 6-port and 14-port microchannels with hydraulic
diameters of 1.54 mm and 1.02 mm, respectively. Fluids and saturation temperatures used in this experimentation
include carbon dioxide at 15ºC, ammonia at 35ºC, and R245fa at 40ºC. Two-phase flow conditions include mass
fluxes from 50 to 440 kg/s.m2 and qualities varying from 0 to 1.
Experiments indicate that two-phase pressure drop and void fraction are dependent upon hydraulic
diameter, mass flux, quality, and vapor density. Two-phase pressure drop is most significantly influenced by inertial
force of the flow. Void fraction is strongly influenced by flow regime, which can be related to the vapor density of
the refrigerant. In general, models exist to predict the experimental two-phase flow pressure drop and void fraction
satisfactorily for specific conditions, but no comprehensive model has been formulated that encompasses the
physical properties defining two-phase flow.

Issue Date:

2003-12

Publisher:

Air Conditioning and Refrigeration Center. College of Engineering. University of Illinois at Urbana-Champaign.